Offshore structures are considered as fail safe and inspections are carried out during their service lifetime to assess their actual condition. In this paper, the effect of inspection updating on fatigue reliability of offshore structures is investigated. In particular, the effect of inspection on the reliability of both inspected and uninspected joints is assessed dependent upon the correlation of properties of different joints. The effect of repeated inspections and inspection sample size on fatigue reliability is also investigated. The influence of inspection of certain joints on the reliability of a series system is studied and the effect of system-based updating policy on fatigue reliability is investigated. It is found that the system reliability is significantly affected by the inspection updating policy. [S0892-7219(00)00403-9]

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The Steel Catenary Riser (SCR) concept offers advantages over other riser concepts and has been widely deployed worldwide. The first deepwater SCR was installed in the Gulf of Mexico in 1994. Since then, more than 100 SCRs have been installed for many types of deepwater floaters (Spars, TLPs, SEMIs, and FPSOs) in the deepwater fields of West of Africa, the Gulf of Mexico (GoM), and Offshore Brazil. As the second of two companion papers, this paper presents the state-of-the-art of key analysis techniques of deepwater SCRs while the first paper addresses the design methodology [R. Song, P. Stanton, Ref. 4]. First of all, the procedure for analysis of deepwater SCRs is discussed and presented in more detail than given in the first paper and is also illustrated in an analysis flowchart. Wave theory applicable to deepwater SCR analysis and time domain vs. frequency domain analysis approaches are described and discussed. More focus is given to the strength analysis including discussion and comparison of regular wave and random wave approaches. Attention is paid to the vortex induced vibration (VIV) analysis including discussion of modal response analysis and VIV parameter selections. For SCRs on semisubmersibles and FPSOs, vessel heave-induced VIV needs to be taken into account, and a corresponding time-domain approach is presented. Similarly, for Spars and deep draft semisubmersibles, vortex-induced motion (VIM) fatigue damage of SCRs is discussed in more detail. Particular attention is also given to the analysis of SCR compression in the touch-down zone (TDZ) and corresponding acceptance criteria are presented. The application of fracture mechanics to engineering criticality assessment (ECA) is explored. Two examples of deepwater SCRs corresponding to a semi and a Spar are given to illustrate the presented methodology.

Steel Catenary Riser (SCR) concept offers great advantages over others and has been widely deployed worldwide. The first deepwater SCR was installed in the Gulf of Mexico in 1994. Since then, more than 100 SCRs have been installed for many types of deepwater floaters (SPAR, TLP, SEMI, and FPSO) in the deepwater fields of West of Africa, Gulf of Mexico, and Offshore Brazil. This paper presents the state-of-the-art of the design methodology of deepwater SCRs. First of all, the design procedure is discussed and is also illustrated in a flowchart. Material selection is discussed in terms of weldability, corrosion resistance, and effect on riser performance. Different wall thickness sizing criteria and design codes are compared. The three most commonly used types of SCR hang off system (flex joint, stress joint, and pull tube) are presented and their application limitations are discussed. Strakes and fairings are discussed and compared as the vortex induced vibration (VIV) suppression devices. Focus is given to the design of SCR global configuration and riser routing. Effect of different floaters on the global configuration design is discussed and illustrated through examples. Thermal performance requirements versus riser global response are traded off. Corrosion, thermal insulation, and anti-abrasion coating materials available for deepwater SCRs are summarized. SCR cathodic protection design methodology is summarized and a design guideline is given. The number one challenge of deepwater SCR design is fatigue. Selection of SN curve, effect of sweet and sour service on fatigue performance, stress concentration factor (SCF) calculation, full scale fatigue testing requirements, application of fracture mechanics to engineering criticality assessment (ECA) is discussed. Fatigue mitigation design is also explored supported by examples. Design of the SCR subsea interface to flowline and pipeline is presented.

With the successful deployment of the five Cascade & Chinook free standing hybrid risers (FSHRs) in the Gulf of Mexico at a water depth of 8,250 ft in year 2010, hybrid riser technology is adopted for deepwater development worldwide. It is basically a combination of steel and flexible risers with utilization of their advantages and hence offers unique features. The Cascade & Chinook FSHRs set a few new world records such as the deepest installed hybrid risers, first disconnectable hybrid risers, first hybrid riser in severe environmental conditions in the GoM, first hybrid riser designed to accommodate two floater concepts. Compared to other installed hybrid risers worldwide, the Cascade & Chinook FSHRs posed more technical challenges and hence required more engineering effort to come up with robust engineering solutions. This paper addresses the engineering challenges and solutions associated with the detail design of the Cascade & Chinook FSHR system including global configuration, material selection and sizing, component design, global and local analysis, and qualification testing. A brief description of the Cascade & Chinook hybrid riser system is given first together with the highlights of the technical challenges. Secondly, factors affecting the global configuration and local component design are identified and evaluated. The logical procedure for design and analysis of deepwater FSHRs is discussed and presented in more detail. Thirdly, focus is given to the global response analysis including strength and fatigue as well as local finite element analysis of components such as the taper stress joint, buoyancy can, riser top, lower assembly and foundation pile. Discussion is also given to the relationship between engineering design, fabrication and installation, which is of particular interest for this type of riser. And in conclusion, some important lessons learnt from the execution of the Cascade & Chinook FSHR engineering are summarized. 1. INTRODUCTION In recent years, exploration and production activities have increased dramatically in deep and ultra-deep water, nearly tripling the water depth of production facilities in the last decade or so. The targeted water depths for oil and gas developments in areas such as the Gulf of Mexico (GoM), West of Africa (WoA), and Brazil are increasing every year. Among the field proven riser concepts shown in Figure 1-1, hybrid risers offer certain unique advantages [Ref. 4] over other concepts such as steel catenary risers (SCRs), top tension risers (TTRs) and flexible risers (FRs) for specific applications.